A pool boiling experiment was conducted to investigate the relation among contact angle, bubble diameter, and critical heat flux. Infrared(IR) thermometry was employed to measure the bubble diameter directly in pool boiling experiment conducted on Si and Teflon surface by visualizing the liquid-vapor interface through IR-transparent silicon substrate. Critical heat flux on Si and Teflon surface were about 1,200kW/m² and 160kW/m², respectively. It was observed that bubble behaviors, i.e., nucleation site density, bubble frequency, and bubble diameter, were drastically changed with respect to contact angle conditions at the same heat flux condition. The bubble diameter decreases as the applied heat flux increases and as contact angle decreases.